During the last decade serious attention has been given to replacing the drill and blast technique for tunneling, mining and similar operations. One alternative technique involves the use of high velocity jets of water or other liquid to fracture the rock or ore body and numerous devices intended to produce pulsed or intermittent liquid jets of sufficiently high velocity to fracture even the hardest rock have been suggested. Devices of that type are disclosed in for example U.S. Pat. Nos. 3,784,103 and 3,796,371. As yet, however, jet cutting techniques are still unable to compete with the traditional methods of rock breakage such as drill and blast in terms of advance rate, energy consumption or overall cost. Moreover serious technical problems such as the fatigue of parts subjected to pressures as high as 10 or 20 kbar and excessive operational noise remain.
A second, and even older technique for fracturing the rock and for saturating soft rock formations such as coal with water for dust suppression involves drilling a hole in the rock and thereafter pressurizing the hole with water either statically or dynamically. This technique is disclosed in for example German Patent Nos. 230,082, 241,966 and 1,017,563.
These methods are inapplicable to hard rock formations because of the restriction in working pressure which can be realized or usefully utilized with conventional hydraulic pumps. They are difficult to apply in practice particularly in soft crumbling rock or badly fissured rock in that the bore hole must be effectively sealed around the tube introduced into the hole through which the liquid is pumped. These restrictions in all make the method far less versatile than drill and blast.
It is an object of the invention to provide method and means for breaking hard compact material such as rock by pulsed or intermittent jet devices which are operated to hydraulically pressurize holes having been drilled into the material beforehand. Particularly, the present invention seeks to provide method and means of the above mentioned type wherein the generation and driving of the material or rock breaking cracks can be controlled more effectively under the high stagnation pressure created in the hole. Another object of the invention is to improve during operation the alignment of the nozzle with respect to the hole to be pressurized by the liquid jet. A further object is to provide more dependable material or rock fracturing in case of defective configuration of the pre-drilled holes. A still further object is to decrease the noise of the jet by confining jet emission to the interior of the hole.